Blackwelder column: Fire blight harming trees

  • Posted: Friday, May 17, 2013 12:24 a.m.
Fire blight is harming local trees.
Fire blight is harming local trees.

Many have called distressed about blight on their Bradford pears, fruiting pears and apple trees. The unusually cool, damp weather experienced a month ago has caused both ornamental and fruit trees to look as though their limbs have been singed with a torch. The problem is most likely fire blight.

Blossoms, fruits, fruit spurs, twigs, and branches are affected and sometimes the entire tree may be killed. Many are calling, concerned that the trees may die.


Fire blight is a bacterial disease that can severely damage apples and pears. The bacteria will over-winter in diseased and dead tissue or cankers. The disease develops rapidly in conditions of cool weather combined with high humidity or rainy weather. In the spring, bacteria are often carried by wind, rain and insects to blossoms or succulent shoots.

Bacteria enter through natural openings in the flower or through stomata in the leaves; however, wounds and injuries made by insects, hail, and wind or by pruning are important means of entrance. Under ideal conditions, the bacteria may be carried to other blossoms, twigs or fruits resulting in secondary infections. During bloom, bees can carry the fire blight bacteria during pollination.

Control of this disease is not easy. Planting resistant varieties is a logical choice to reduce use of pesticides and continual pruning. Although varieties vary in resistance to fire blight, none are immune. This next step is to remove of all cankers and blighted twigs before growth starts in the spring. Cuts should be made 4-6 inches beyond any evidence of dead tissue. Cuts should be made 10-12 inches beyond the last evidence of disease. Care must be taken to prevent spread of the bacteria by hands or cutting tools. If infections are cut out, use bleach (Clorox) dilute 1:10 with water to sterilize pruning shears or saw blades between each cut.

Streptomycin sprays will help control the disease in tree fruits of pear and apple, however this must be done while the tree is blooming in March. Sprays before, during and after bloom are very important for control. Streptomycin will not harm the bees.

Take time to remove succulent, rapidly growing twigs and shoots during the summer. These are most susceptible to infection. Over fertilizing using excessive amounts of nitrogen fertilizer produces excessive growth and watersprouts, which develop near the base of the scaffold limbs, crotch, or trunk. Go online to http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2208.html for more detailed information.

Darrell Blackwelder is Rowan County’s Extension Director. Call 704-216-8970.

www.rowanmastergardener.com

rowan.ces.ncsu.edu

www.rowanextension.com

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